The present invention relates to the manufacture and application of capacitive touch screen electrode layers by the use of single layer fine-line metal mesh electrodes printed onto a substrate. The method includes a simple way to self-test the electrodes from a connector so as to avoid the need for more elaborate test methodologies.
Most touch screens today, capacitive or otherwise, use a sputtered layer of Indium Tin Oxide (ITO) deposited onto a thin plastics film (such as PET film) or directly onto a glass layer. The ITO is uniformly deposited then etched using a subtractive process which involves numerous process steps. Finally, layers of silver ink and dielectric are used to make connections to the ITO on film or glass, which adds yet more process steps.
ITO films are clear to about 92% (single layer), but have a relatively high resistance and are known to be quite fragile. A relatively high percentage of films become damaged during production, requiring an expensive and time-consuming test stage. Also, ITO films are expensive and there are only a few suppliers who can competently manufacture such films, causing logistical problems for users of these films. Finally, Indium is a scarce metal which is increasingly in demand, yet production of this metal is limited by the few mines which produce it.
Other materials can replace these films, such as poly(3,4-ethylenedioxythiophene) or PEDOT conductive polymer. However PEDOT is not as optically clear as ITO, is difficult to deposit uniformly, and degrades rapidly under adverse environmental conditions.
Therefore there is a need for a new material and/or method for producing touch screens which overcomes the above limitations.